The invention concerns a method of operating a furnace in which a radiation screen wall is installed between a melting area and a refining area with a refining bank. This radiation screen wall leaves free at least one flow channel above the surface of the glass melt for a countercurrent flow of at least a part of the combustion gases from the refining area to the melting area.
U.S. Pat. No. 4,932,035 describes such a glass melting furnace. It is mainly used to ensure that the glass remains fluid during discontinuous operation, by means of internal heat exchange between the waste gases from the burners and the glass melt, and to bring the glass to the necessary working temperature quickly and very efficiently after a re-start of operation. A first radiation screen wall, installed in the melting area, the lower edge of which wall being just above the charging material, contributes to the complete melting out of the charging material by means of the counter-flow of the hot combustion gases. A flow channel for the combustion gases in a second radiation screen wall, installed immediately in front of the refining area, does not produce any appreciable heat exchange, as the lower edge of this flow channel is at a noticeable distance from the glass melt.
In the aforesaid solution a difficult-to-cool bottom outlet channel for the glass melt is installed in the middle of the furnace and in front of the refining bank. Such bottom outlet channels are considerably narrower than the furnace bottom and/or the distance between the side walls of the furnace and therefore have a small flow cross section. Therefore there is a high flow velocity in the bottom outlet channels which results in intense corrosion of the hot surrounding walls which are made of mineral materials.
U.S. Pat. No. 4,882,736 describes a glass melting furnace in which bottom electrodes are installed below the charging area at a great distance from the refining area. These bottom electrodes produce an upward current, which introduces additional melting heat from below into the charging material. As indicated on the drawing by the flow arrows, the upward current at this location not only has no influence on the processes in the refining area, but it also slows the return flow of the glass melt and does not have any synergistic interaction w with the counter-flow of the combustion gases, i.e., the gases are drawn off before they reach the upward current of the glass. Therefore, the charging material is neither heated simultaneously nor at the same location by the combustion gases from above or by the bottom electrodes from below. Neither is a radiation screen wall, the bottom edge of which could form a flow channel for a counter-flow of the combustion gases, installed above the bottom electrodes.
Downstream of these bottom electrodes, the furnace bottom rises gradually in the shape of a long ramp to the height of the refining bank, on the upper side of which a step is installed. The step is "straddled", so to speak, across the angle between the sloping furnace bottom and the refining bank. The step, therefore, has a volume regulating function and does not increase the effect of the bottom electrodes, which are installed in the charging area at a significant distance upstream of the step. The surface of the refining bank situated behind the step must therefore be at a greater distance from the melt surface, which works contrary to the effect of the refining bank. With this technology, it is the bottom of the melting area that produces a flow pattern, through which the hot glass on the bath surface flows back to the floating batch layer. However, this produces a surface flow, which continually moves glass, heated intensively by the burners, from the refining area into the charging area. This causes currents that are difficult to control and flow in opposite directions above the raised area, as in fact charging material is being added continually, and molten glass must be extracted from the furnace. This has a further, very significant disadvantage, already refined, i.e., pure molten glass, is re-introduced into the charging and melting area, where it comes into contact with the charging material and must then be refined again.